Electric discharge apparatus



Aug. 22, 1.939. M. A. EDWARDS ELECTRIC DISCHARGE AEPARATUS I Filed March22, 1938 Inventor:

Martin A. Edwards,

His Attorney.

Patented Au 22, 1939 UNITED STATES anaemic mscnaacn maaa'rus Martin A.Edwards, Schenectady, N. Y., alsigncr to General ElectricOompany, a orpration of New York Application March 22, 1938, sci-nu No. 191.5%:

11 Claims. (01. rte-124) m invention relates to gaseous electricdischarge devices and apparatus for operating the same from alternatingcurrent circuits. It relates particularly to electric discharge deviceswhich require the application of a higher voltage for starting them thanfor the subsequent operation thereof. Certain forms of apparatus of thischaracter which have been constructed heretofore and which have includedcapacitors for obtaining the required higher starting voltage have notbeen entirely satisfactory for various reasons; the cathodes of thedevices often have been damaged by the high current peaksproduced by thecapacitors employed, and the apparatus has not had as good operatingcharacteristics as desired.

One object of my invention is the provision of improved. apparatus ofthe above mentioned character which employs simple means includingcapacitors by which the desired starting voltage may be obtained withoutdanger of damage to the cathodes. Another object is the provision ofimproved apparatus of this character which will operate with highefliciency and good stability which will not be critical to reasonablevariations in line voltage and whose construction will be simple andinexpensive to manufacture.

My invention will be betterunderstood from the following descriptiontaken in connection with the'accompanying drawing and its scope will bepointed out in the appended claims.

Referring to the drawing, Fig. 1 is a circuit diagram illustrating oneembodiment of my invention in which an electric discharge device is em--ployed having non-thermionic electrodes; Fig. 2 is a circuit diagramillustrating a modification thereof; Figs. 3 and 4 are circuit diagramsshowing modifications in which the discharge device is provided withthermionic electrodes, and Fig. 5 is a circuit diagram illustrating afurther modiflcation wherein two discharge devices are connected inseries, each device being provided with thermionic electrodes.

While my invention is applicable to apparatus employing various forms ofelectric gas discharge devices it is of particular interest and has beenespecially developed for use in connection with low pressure dischargedevices which are employed to give light. A preferred form of suchdevice is a lamp of the positive column type comprising a tubularenvelope having electrodes at its ends and containing a gaseousatmosphere such as a few millimeters of a rare gas, for example argon,and a small quantity of a vaporizable meta! such as" mercury. Preferablythe envelope is coated internally with a suitable fluorescent materialin order that the electric discharge, which in itself may be scarcelyvisible, shall produce the desired high degree of illumination. Thecoating may also contain a suitable material to cause the lamp tocontinue to give light during the intervals of current reversal therein.In the description to follow, therefore, I shall refer to the dischargedevices as lamps. It is well known that to start a discharge in such alamp by the application of a voltage to its electrodes a higher voltagemust be employed than that required to maintain the discharge after ithas been started.

Referring to Fig. 1, I have shown the electric discharge device or lampat i, the same being provided at its ends with the thermionic electrodes2 and 3 which are heated by the discharge which takes place between themrather than being previously heated to an electron emitting temperatureas, for example, by passing 8. current through them. Before starting,the lamp has a high resistance and may require a voltage considerablyhigher than that of the circuit from which it issupplied to start adischarge therein.. A 'lampfor example that is adapted to operate on a115 volt circuit may require the application of approximately 300 voltsbetween its electrodes to cause it to start. After it has startedhowever,-the arc drop will be approximately only volts but a voltagesomewhat greater than that is required to maintain the discharge. Thisrequired voltage 'has been found to be of the order of the v times thevoltage of the arc .drop. In the circults now to be described thediiference between v the voltage of the source of supply and the arcdrop voltage is absorbed by the ballast employed.

The lamp is shown connected withthe source of supply 6 of alternatingcurrent which, for example, may be a 60 cycle, volt lighting circuit bythe connections 4 and 5.- These connections include ballast'devicescomprising the reactor or choke coil 1 which, for example, may have aninductance of 1.2 henries and the capacitor 8 which, for example, mayhave a capacitance of 3 mid., the reactor and capacitor being arrangedin series with the lamp. Connected across the lamp is a second reactoror choke coil 9 which, for example, may have an inductance of 1.4henries. Energization of the lamp circuit may be controlled by anysuitable switch'such a switch being illustrated by way of example at It.

When the switch It is closed to energize the lamp, thereactor i, thecapacitor 8 and the reactor 9 constitute a circuit which is in acondition of partial resonance, that is, the inductance and thecapacitance of the circuit are not such that the circuit is tuned orinexact resonance at the frequency of the source of supply but rather isonly partly tuned or, in other words, is operated oil-the resonancepeak. As a result of that condition the voltage across the reactor 9 andhence the voltage applied to the electrodes of the lamp is raisedconsiderably above that'of the supply circuit and is suficient to causea discharge to start in the lamp. As soon as the discharge starts thereactor 9 is substantially short circuited by the lamp inasmuch as theimpedance of the lamp is materiallyless than that of this reactor. Thelamp continues tooperate therefore on the circuit comprisingsubstantially only the reactor 5 and capacitor 8, and inasmuch as thereactance provided by the capacitor predominates over the reactanceproduced by the reactor 1 the lamp, in effect, operates withcapacitative ballast; hence the apparatus draws a leading current fromthe supply circuit 6. If desired, the reactor 9 may be constructed tosaturate before the discharge in the lamp starts but I prefer it shallnot saturate.

I. have found that when a capacitor is em-- results are apparent in theelectrodes of the lamp. 1 In the modified form of my inventionillustrated by Fig. 2 the reactor i2, which for example may have a.value of 2.6 henries is arranged to shunt both the lamp i and thereactor i3 whose reactance may be 2.6 henries. In series with the lampis the capacitor it whose capacitance may for example be 3 mid. In thiscase when the switch ill is closed to start the lamp thecircuitincluding the capacitor M and the reactor 52 is-in partial resonance;hence the voltage across the reactor i2 is raised sufliciently to causea discharge to start in the lamp. As soonas this occurs the reactor l2becomes shunted by the lamp and the reactor i2. Since the lamp currentnow passes in series through the capacitor and the reactor i3 and sincethe reactance of the capacitor predominates .over that of the reactor ISthe lamp operates with capacitative ballast and hence draws a leadingcurrent from thesource 6 as in Fig. 1. The reactor i3 also serves toabsorb and smooth, out the high current peaks produced by the capacitorthereby saving the lamp cathodes from damage.

In the modification shown by Fig. 3 the electrodes i5 and it areinitially heated to an electron emitting temperature by passing acurrent through them. In this case I also employ in series with the lampthe reactor ii whose inductance, for example, may be 1.2 henries and thecapacitor l8 whose capacitance may, for example be 3 mid. Connectedacross the lamp is the reactor !9 whose'inductance, for example, may be1.2 henries, the reactor in this case however being arranged in serieswith the electrodes 65 and i6 whereby before the lamp starts theresonance 'spot formed thereon.

current that passes the reactor I! also traverses the two electrodes andheats them.

. start therein. It having started, the reactor it is substantiallyshort circuited by the lamp and the electrodes are kept hot chiefly bythe cathode The lamp then operates with capacitative ballast and theelectrodes are protected by the reactor l6 from current peaksoriginating in the capacitor.

That form of my invention illustrated by Fig. 4 also has initiallyheated electrodes and the circuit is similar to that shown in Figs. 1and 3 except that instead of employing a reactor to shunt the lamp, Iemploy a split core transformer, that is, a transformer having an airgap in its magnetic circuit, whose primary 20 shunts the lamp and whosetwo secondaries 22 and 23 are connected to supply heating current to thelamp electrodes. In this case the series reactor 24 may have aninductance, for example of 1.2 henries. the capacitor 25 may have acapacitance for example of 3 mfd. and the primary 20 may have aninductance of 1.4 henries. As in the forms of my invention previouslydescribed, the primary 20, before the lamp starts, forms with thereactor 24 and the capacitor 25 a circuit in partial resonance whereby asufficiently high voltage is ap-. plied to the electrodes of the lamp tostart a discharge therein and a heating current proportional to theresonance current is supplied to the electrodes. During the subsequentoperation of .the lamp the voltage across the primary 20 of thetransformer is insufllcient to produce an appreciable heating current inthe two secondary windings thereof but the lamp electrodes aremaintained at an electron emitting heat by the cathode spot formedthereon.

The modification illustrated by Fig. 5 is similar to that of Fig. 3except that two lamps i and i' are shown in series, each lamp beingshunted by a. separate reactor l9 and iii. In this case the seriesreactor H1 and capacitor l8 may, for example, have the same values asthe corresponding parts of Fig. 3. Reactors i9 and I9 however, eachmayhave an inductance, for example of 0.7 henries. In this modificationreactors I9 and 59 together with reactor I l and capacitor i8 form thecircuit in partial resonance, otherwise the operation of thismodification is similar to that shown by ,Fig. 3, hence a furtherdescription thereof seems to be unnecessary. While in Figs. 1 and 2 Ihave not shown any means for initially heating the electrodes, it willbe understood that the electrodes may be heated if desired at startingby supplying current thereto from any suitable source.

I have chosen the particular embodiments described above as illustrativeof my invention and it will be apparent that other modifications may bemade without departing from the spirit and scope of my invention whichmodifications I aim to cover by the appended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In combination, a source of alternating current supply, a circuitcomprising a capacitor and a reactor connected across said source, anelectric discharge device having a starting voltage higher than saidsource connected to receive the 3. In combination, a source ofalternating cur-' rent supply, an electric discharge device connected tobe supplied therefrom, a capacitor and a reactor arranged in series insaid connection and a reactor connected across said discharge device.

4. In combination, a source of alternating current supply, an electricdischarge device connected to be supplied therefrom, capacitativeballast for said device in said connection, means in said con-'thermionic electrodes, a ballast capacitor and a reactor connected inseries between said source.

and said device and a second reactor connected between said electrodesand forming a series circuit therewith.

7. In combination, a source of alternating current supply, an electricdischarge device having thermionic electrodes, means connecting saidsource with said electrodes including a ballast capacitor and asmoothing reactor arranged in series, a transformer having a primaryconnected across said device and a plurality of secondaries and meansfor supplying current from said secondaries to said electrodes to heatthe same.

v8. In combination, a source of alternating current supply, a circuitconnected to be supplied therefrom having capacitative and inductiveelements arranged in series and 'an electric discharge device in shuntrelation to one of said elements, the inductive reactance in saidcircuit being materially less than the capacitative reactance thereinwhereby a condition of resonance does not occur and excessive currentflow in the circuit is avoided.

9. In combination, a source of alternating current supply, an electricdischarge device having a starting voltage higher than the voltage ofsaid source, means including a ballast capacitor connecting said deviceacross said source, a reactor cooperating with said capacitor forraising the voltage supplied to the device from said source and. areactor in circuit with said device for smoothing out current peaksarising in said capacitor.

10. In'combination, a source of alternating current supply, a circuitconnected to be supplied therefrom including a-capacitor and a reactor,an electric discharge device having a starting voltage higher than thevoltage of said source connected to receive the voltage across saidreactor, the amount of capacitance in the circuit being more than thatrequired to produce a condition of resonance therein and means incircuit

